The present invention relates to a shock absorber configured to generate a damping force against a stroke of a piston rod.
Generally, a tubular hydraulic shock absorber mounted on a suspension apparatus of a vehicle, such as an automobile, is configured in such a manner that a piston with a piston rod coupled thereto is slidably fitted in a cylinder sealingly containing fluid, and a damping force adjustment mechanism including an orifice, a disk valve, and/or the like controls a flow of the fluid that is caused by a sliding displacement of the piston in the cylinder, thereby generating a damping force against a stroke of the piston rod.
Further, a hydraulic shock absorber disclosed in Japanese Patent Public Disclosure No. 2006-38097 includes a backpressure chamber (a pilot chamber) formed behind a disk valve, which is a damping force generation mechanism, with a flow of fluid partially introduced into the backpressure chamber to apply an inner pressure in the backpressure chamber in a direction causing the disk valve to be closed.
Then, this hydraulic shock absorber controls valve opening of the disk valve by adjusting the inner pressure in the backpressure chamber. This configuration can enhance flexibility in adjusting a damping force characteristic.
In the above-described shock absorber disclosed in Japanese Patent Public Disclosure No. 2006-38097, the backpressure chamber is formed by fixedly attaching a ring-shaped seal member made of an elastic member, such as a rubber, to an outer circumferential portion of a back surface of the disk valve by vulcanization, adhesion, or the like, and slidably and liquid-tightly fitting this seal member to a cylindrical portion of a bottomed cylindrical member disposed behind the disk valve.
The disk valve configured to use the ring-shaped seal member fixedly attached to one side in this manner necessitates a sufficient increase in a pressing force applied to a sliding portion to ensure a sealing performance of the seal member. However, the increase in the pressing force leads to an increase in a sliding resistance accordingly. A set load (a preload) is provided, i.e., the disk valve is seated on a seat portion while being deflected in advance to prevent this sliding resistance from making it difficult to close the disk valve, so as to ensure that the disk valve can be closed by being seated on the seat potion at the time of valve closing.
However, in recent years, the damping force adjustable shock absorber mounted on the suspension apparatus of the vehicle, such as the automobile, has been subject to a demand of sufficiently reducing the damping force in a region where a piston speed is low when the damping force characteristic is switched to a soft side, and providing the set load to the disk valve works against this demand.